Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Blood dilution during bypass surgery associated with kidney damage

03.09.2003


When physicians routinely "thin" the blood of patients undergoing coronary artery bypass surgery in order to place them on the heart-lung machine, they may be causing more damage to the kidneys and other organs than previously appreciated, according to a new study by Duke University Medical Center researchers.



For years moderate dilution of the blood has been thought to protect the kidneys from damage, but the Duke researchers found in their study of more than 1,400 bypass patients that dilution to the lower levels of accepted ranges is associated with measurable kidney damage. The Duke team published the results of its study in the September 2003 issue of the Annals of Thoracic Surgery.

In order to safely operate on a non-beating heart, physicians attach the body to a heart-lung machine, which takes over for the stopped heart in circulating oxygen-rich blood throughout the body. To prime the pump, physicians add fluid -- usually a balanced saline solution -- to the circuit to fill the tubing and pumping chambers of the machine.


This additional fluid lowers the percentage of oxygen-carrying red blood cells in the blood, a measurement known as hematocrit. Normal hematocrit ranges from 36 to 40 percent. During bypass surgeries, the hematocrit can range from 22 to 26 percent, with even lower percentages being commonly attained at different points during the operation.

"Using hematocrit as a tool to assess a patient’s anemia, we found that the lowest hematocrit achieved during the bypass procedure was significantly associated with acute kidney damage," said Duke anesthesiologist and study leader Mark Stafford-Smith, M.D. "Furthermore, we found the risk to kidneys increases as a patient’s body weight increases.

"This is the first report highlighting the association of hemodilution during bypass surgery with acute injury to the kidneys," Stafford-Smith continued. "Our findings question the wisdom of tolerating the lowest levels of hematocrit during bypass surgery."

Transfusing additional blood is not considered an ideal solution, Stafford-Smith said, since this and other studies have shown that transfusions are also associated with kidney damage. He recommended that more attention be paid to shortening the bypass circuit or using smaller diameter tubing to reduce the levels of hemodilution.

Every year, more than 750,000 patients worldwide undergo bypass surgery, and researchers estimate that about one of every 12 will suffer kidney damage as a result of the surgery. While most cases of kidney injury are transient, up to 2 percent of bypass patients will require kidney dialysis, with 60 percent of those dying before hospital discharge, Stafford-Smith said.

One commonly accepted benefit of hemodilution has been that it makes the blood less viscous, Stafford-Smith said. Also, it has been thought that since body temperature is lowered during surgery, there were enough red blood cells in the diluted blood to satisfy the tissue’s reduced need for oxygen. Stafford-Smith said that the physicians want to minimize the use of donated human blood to prime the heart-lung machine pump.

Other studies have suggested that the lowest hematocrit levels reached during surgeries may be linked with worse outcomes, so Stafford-Smith and his colleagues consulted the medical records of 1,404 patients receiving bypass surgery at Duke University Hospital to answer the question.

He correlated hematocrit levels during surgery with levels of creatinine -- a byproduct of normal metabolism -- in the blood before and after surgery. Kidneys normally filter creatinine out of the blood and excrete it in the urine, so higher-than-normal levels in the blood indicate that the kidneys’ ability to filter blood has been impaired.

Interestingly, the researchers found a strong link between the weight of patients and increases in the levels of creatinine in the blood.

"For example, for a patient weighing 165 pounds, there is no association between lowest hematocrit and increased creatinine," Stafford-Smith said. "However, in the 330-pound patient, there is a highly significant inverse association. The significance of the association rises as weight increases.

"For this reason, it is important for physicians to pay special attention to their patients who are overweight or who have existing kidney damage," he said.

Stafford-Smith pointed out that up to 20 percent of patients who are scheduled for bypass surgery have some degree of existing kidney damage, further emphasizing the need for physicians to consider these factors in the care of their patients.

The researchers also looked at the role of transfused blood during bypass. They came to the conclusion that if it seems likely during the course of the procedure that the patient will require a later transfusion, it is best to give that blood before the hematocrit drops to the lowest levels.

"The level of a patient’s hematocrit is a factor that we as physicians have control over, and it is also a factor that is amenable to proper management," Stafford-Smith.

In the course of their studies, the researchers also followed minute-by-minute changes in blood pressure during the period of support on the heart-lung machine and were surprised to find that changes in blood pressure had little effect on kidney damage.

Stafford-Smith’s analysis of the data was supported by the cardiothoracic division of the Duke’s department of anesthesiology.

Members of Stafford-Smith’s Duke team were Madhav Swaminatham, M.D., Barbara Phillips-Bute, Ph.D., Peter Conlon, M.D., Peter Smith, M.D., and Mark Newman, M.D.

Richard Merritt | EurekAlert!
Further information:
http://www.dukemednews.org/

More articles from Health and Medicine:

nachricht Laser activated gold pyramids could deliver drugs, DNA into cells without harm
24.03.2017 | Harvard John A. Paulson School of Engineering and Applied Sciences

nachricht What does congenital Zika syndrome look like?
24.03.2017 | University of California - San Diego

All articles from Health and Medicine >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

Im Focus: Researchers Imitate Molecular Crowding in Cells

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

Argon is not the 'dope' for metallic hydrogen

24.03.2017 | Materials Sciences

Astronomers find unexpected, dust-obscured star formation in distant galaxy

24.03.2017 | Physics and Astronomy

Gravitational wave kicks monster black hole out of galactic core

24.03.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>